Recognizing that icing of the evaporator heat exchanger in a consumer or commercial refrigeration unit, such as a refrigerator or freezer, many modern appliances provide fixed or adaptive defrost control. Such a defrost control provides heating of the evaporator heat exchanger so as to melt any accumulated frost or ice that may have formed thereon during the refrigeration cooling cycle. Many different methods of controlling the defrost cycle are known in the art, including electromechanical timers and microprocessor control.
Typically, such defrosting circuitry employs a heater positioned in proximity to the evaporator heat exchanger within the freezer compartment of the refrigerator or freezer. At controlled intervals while the refrigeration system is not operating during its normal temperature control cycle, the defrost heater is energized. This defrost heater generates enough heat to cause melting of the frost build up or ice on the evaporator heat exchanger, which greatly increases the efficiency of subsequent cooling cycles.
While providing a defrost heater greatly enhances the overall efficiency of the refrigeration cycle, the heat generated by the defrost heater will have to be removed in subsequent cooling cycles to maintain the interior temperature of the freezer compartment. A simple rule of thumb is that twice the amount of energy is needed to remove a unit of heat. As such, heat generation within the freezer compartment must be minimized both during the defrost cycle, and when the defrost heater is not energized.
Electromechanical defrost timers and modern adaptive defrost controls operate to provide such limited heating only when necessary and only to the extent necessary to accomplish the defrosting of the evaporator heat exchanger. During other periods, the defrost heater is turned off, although the defrost heater control circuitry is still powered. Unfortunately, even when the defrost heater is turn off, this control circuitry still generates a small amount of heat due to the consumption of the standby power by the control circuitry when not in the defrost mode of operation. While small, this heat generated must still be removed during subsequent cooling cycles. As a result, the overall efficiency is decreased and the cost of ownership of the appliance is increased.
There exists, therefore, a need in the art for a refrigeration defrost control circuit that reduces the amount of heat generated while in this standby mode of operation when the defrost heater is not energized. The circuitry of the present invention provides such power reduction.
These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.